Highly reactive oxygen species such as superoxide anion (0.sub.2.sup.-), hydrogen peroxide (H.sub.2 0.sub.2), hydroxyl radical (.OH), and lipid peroxides (LOOH) are involved in a number of human diseases. For example, oxygen radicals have been implicated in autoimmune diseases, arthritis, tissue damage caused by environmental pollutants, cigarette smoke and drugs, tissue injury during surgery and transplantation, as well as a variety of other conditions (Halliwell, B., Fed. Amer. Soc. Exp. Biol. 1:358-364, 1987).
Reactive oxygen species are also generated during the response to injury by phagocytic cells. One of the early events in the wound healing response is the cleansing and sterilization of the wound by neutrophils and macrophages. A mechanism for this sterilization is the generation of the highly reactive superoxide anion and hydrogen peroxide. Superoxide anion and hydrogen peroxide will, in the presence of iron or other redox active transition metal complexes, generate hydroxyl radical. The hydroxyl radical is a potent oxidant which will initiate the free radical oxidation of fatty acids and the oxidative degradation of other biomolecules.
One of the most vital areas in which reactive oxygen species cause tissue damage is in post-injury damage to the brain and spinal chord, and in reperfusion injury to ischemic tissue following surgery and transplantation (e.g., the heart). A sudden inrush of oxygenated blood and activated phagocytic cells leads to superoxide anion and hydrogen peroxide formation. These species do direct damage to the tissue and also react with iron, as discussed above, to generate the very reactive hydroxyl radical.
Iron has also been shown to have a direct role in the initiation of lipid peroxidation. An Fe(II)/Fe(III) complex can serve as an initiator of lipid oxidation. In addition, many iron complexes can catalyze the decomposition of lipid hydroperoxides to the corresponding lipid alkoxy radicals, which will continue the peroxidation cascade. The major storage site for iron in serum and tissue is ferritin. This ubiquitous storage protein (M.W..about.450,000) can store up to 4500 atoms of iron per protein molecule. It has been shown that superoxide anion can promote the mobilization of iron from ferritin. This free iron may then catalyze lipid peroxidation and the conversion of superoxide anion to the more damaging hydroxyl radical.
A mechanism for the generation of the hydroxyl radical is illustrated below: ##STR1##
A number of therapeutic agents have been utilized to prevent or limit oxidative damage. For example, agents such as superoxide dismutase (a 32,000 Dalton molecular weight enzyme), anti-oxidants (such as Vitamin E and C), and transition metal chelators have been shown to eliminate these ions and prevent them from participating in free radical reactions. Additional compounds which possess anti-oxidative properties include glycyl-L-histidyl-L-lysine:copper(II) and certain derivatives thereof, U.S. Pat. Nos. 4,760,051, 4,665,054 and 4,877,770, each of which are incorporated herein by reference.
As mentioned above, due to the severity and incidence of disease states in which reactive oxygen species play a role, there is a need in the art for effective anti-oxidant agents. Desirably, such agents should eliminate reactive oxygen species, inhibit the mobilization of metal ions such as iron which may participate in the generation of such species, and be available at the site of injury or reactive species generation.